1. Field of the Invention
The present invention relates generally to bicycles and, more specifically, to a bicycle speed change control device for controlling the gear shifting position of a derailleur of the bicycle.
2. Description of the Related Art
U.S. Pat. No. 5,094,120 disclosed a bicycle speed change control device entitled xe2x80x9cBicycle Speed Change Lever Assemblyxe2x80x9d, which comprises a first lever pivotally pressed to wind up a control cable against a tension applied thereto, a second lever pivotally pressed to pivotally return the first lever for paying out the control cable, and an indexing mechanism provided between the first and second levers for holding the first lever at a selected one of stepwise pivotal positions against the cable tension. The indexing mechanism is made to have a skip preventing function for ensuring that the first lever is pivotally returned stepwise.
This design of bicycle speed change lever assembly is still not satisfactory in function. Because the freewheel gear cluster of an advanced bicycle is comprised a big number of gears, it requires a big angular momentum, resulting in inconvenience of approach of fingers to the two distal ends of the operating range.
Further, because the engagement structure between the second lever and the indexing mechanism is not highly precisely matched, the first lever may be pivotally returned in a rush from the last gear shift position to the first gear shift position, resulting in an improper speed change.
The present invention has been accomplished to provide a bicycle speed change control device, which eliminates the aforesaid drawbacks.
It is therefore the main object of the present invention to provide a bicycle speed change control device, which can be turned forwards through an angle to change the gearshift position, and then returned without changing the gearshift position for a next forward gearshift position control operation.
It is another object of the present invention to provide a bicycle speed change control device, which positively secures the cable control set in position, preventing an engagement skit accidentally.
It is still another object of the present invention to provide a bicycle speed change control device, which drives the cable control set to rotate positively during forward gearshift position control, and enables the cable control set to be smoothly returned upon operation of the second lever to reverse the gearshift position.
To achieve these and other objects of the present invention, the bicycle speed change control device comprises a housing connectable to one handlebar of a bicycle, the housing comprising a first coupling portion and a second coupling portion; a cable control set fastened pivotally with the first coupling portion of the housing and reversibly supported on the first coupling portion of the housing by a torsion spring and adapted to drive the cable to control the gearshift position of a derailleur of the bicycle, the cable control set comprising a first toothed engagement portion, a second toothed engagement portion, and a third toothed engagement portion; a first lever, the first lever comprising a lever body fastened pivotally with the first coupling portion of the housing and reversibly supported on the first coupling portion of the housing by a torsion spring, the lever body of the first lever having a free end terminating in a finger press portion, and a push member provided at one end of the lever body of the first lever remove from the finger press portion of the lever body of the first lever, the push member being forced into engagement with the third toothed engagement portion of the cable control set and to further turn the cable control set when the first lever is turned in one direction, the push member being disengaged from the third toothed engagement portion of the cable control set when the first lever reversed to a predetermined position; and a second lever, the second levers comprising a lever body fastened pivotally with the second coupling portion of the housing and reversibly supported on the second coupling portion of the housing by a torsion spring, the lever body of the second lever having a fixed end pivoted to the second coupling portion of the housing, a free end terminating in a finger press portion, and a tooth disposed adjacent to the fixed end and adapted to engage the first toothed engagement portion and second toothed engagement portion of the cable control set selectively, the tooth of the second lever being moved with the second lever over teeth of the first toothed engagement portion stepwise when the first lever turned to rotate the cable control set forwards, the tooth of the second lever being moved with the second lever into engagement with the first toothed engagement portion and the second toothed engagement portion of the cable control set alternatively for enabling the cable control set to be returned when the second lever alternatively pressed and released.